The present invention relates to a process for preparing a solid state dye laser. More particularly, the present invention relates to a process for preparing a solid state dye laser in a composite glass matrix.
In the last years, an intensive effort have been devoted to obtain solid-state dye laser devices that could replace liquid dye lasers, as described e.g. in R. Reisfeld, Laser based on sol-gel technology, in: R. Reisfeld, C. K. Jorgensen (Eds.), Optical and Electronic Phenomena in Sol-Gel glasses and Modern Application, Structure and Bonding, vol. 85, Springer, 1996, pp. 215-233.
Being compact, non toxic, non volatile, non flammable and mechanically stable, solid-state dye lasers have advantages over liquid dye lasers. Attempts have been made to use polymers as hosts for organic dyes in order to fabricate solid-state dye lasers, but these hosts have been shown to be lacking in mechanical and thermal properties and refractive index uniformity (see, e.g. B. Dunn, J. D. Mackenzie, J. I. Zink, O. M. Stafsudd, SPIE vol. 1328 Sol-Gel Optics (1990) 174).
Sol-gel glass offers a host in which organic dyes can be impregnated into a solid medium. The sol-gel technique is based on hydrolysis and polycondensation reactions of organometallic compounds. In the present case, room temperature reactions of silicon alkoxide Si(OR).sub.4 according to the steps:
hydrolysis: Si(OR).sub.4 +4H.sub.2 O.fwdarw.Si(OH).sub.4 +4ROH PA1 polycondensation: nSi(OH).sub.4 .fwdarw.(SiO.sub.2).sub.n +2nH.sub.2 O PA1 a) preparing a porous silica gel; PA1 b) effecting thermal treatment thereof at a temperature of at least 500.degree. C. to produce a glass with improved mechanical properties; PA1 c) impregnating a solid state laser dye dissolved in methylmethacrylate into said silicon gel glass in a closed container; and PA1 d) effecting heat polymerization of said methylmethacrylate at a temperature of at least 60.degree. C., whereby there is formed a glass having pores impregnated with a solid state laser dye and polymethylmethacrylate.
The result is a cross-linked three dimensional polymer. Generally, tetraethoxysilane, Si(OC.sub.2 H.sub.5).sub.4 (TEOS) or tetramethoxysilane, Si(OCH.sub.3).sub.4 (TMOS) are used as silicon alkoxides. It is common to include an alcoholic or another solvent in the starting mixture and the hydrolysis is generally catalyzed by an acid. Sol particles are produced, condensed and become wet gel and then dry gel. In the last step the gel is condensed and become glass. The porosity of the glass is an important factor and it is controlled by the way of preparation. Quantities and types of catalysts, composition of the starting mixture and temperature of stirring, aging and drying are the parameters which determine the glass porosity.
However, porous glasses are not convenient as laser supporting matrices due to their fragility and due to the low photostability of the dyes when doped in these glasses. In order to fill the pores, incorporation of organic chains is needed. This is currently done in one of two ways: (1) impregnation of an organic polymer (or monomer which becomes polymer after polymerization) in the porous glass. By this way one can obtain composite glasses. (2) Use of a silicon alkoxide compound in which, one of the 4 ethoxy groups of TEOS or methoxy groups of TMOS is replaced by another organic group. This compound can be used as unique alkoxide in the mixture or together with TEOS or TMOS, leading to organically modified silicate (ormosil) glass samples. Compounds like 3-(trimethoxysilyl)propylmethacrylate C.sub.7 H.sub.8 O.sub.2 --Si--(OCH.sub.3).sub.3 (TMSPMA), methyl-triethoxysilane (MTEOS), 3-glycidoxypropyltrimethoxysilane (GLYMO), methyltrimethoxysilane (MTMOS) and vinyltriethoxysilane (VTEOS) are used for this purpose.
In R. Reisfeld, E. Yariv, H. Minti, Opt. Mater. 8 (1997) 31, the present inventors have reported on composite glasses and ormosils doped with perylimide dyes and pyrromethene (PM) 567. We found sensitivity of PM 567 to acidic surrounding, leading to loss of the lasing ability at pH&lt;3 by irreversible process.
Interest in many pyrromethene dyes has been growing due to their high efficiency.
Solid state laser samples doped with pyrromethene dyes, have been investigated, by ormosil, xerogel or sol gel matrices, as reported by B. Dunn, F. Nishida, R. Toda, J. I. Zink, T. H. Allik, S. Chandra, J. A. Hutchinson, Mater. Res. Soc. Symp. Proc. 329 (1994) 267; M. Canva, A. Dubois, P. Georges, A. Brun, F. Chaput, A. Ranger, J.-P. Boilot, SPIE Sol-gel Opt. III 2288 (1994) 298; M. Canva, P. Georges, J. F. Perelgritz, A. Brun, F. Chaput, J.-P. Boilot, Appl. Opt. 34 (1995) 428; M. D. Rahn and T. A. King, SPIE Sol-gel Opt. III 2288 (1994) 382.
Similarly, R. E. Hermes, T. H. Allik, S. Chandra, J. A. Hutchinson, Appl. Phys. Lett. 63 (1993) 877 and Y. V. Kravchenko, A. A. Manenkov, G. A. Matushin, V. M. Mizin, D. P. Pacheco, H. R. Aldag, SPIE Vol. 2986 (1996) 124 report modified polymer matrices using longitudinal pumping system.
Pyrromethene (PM) dyes are high efficiency laser dyes. Heretofore, however, it has not been possible to utilize said dyes in composite glass, which is usually made by impregnation and polymerization of methacrylate (MMA) in silica gel, since polymerization is initiated by benzoil peroxide, which causes damage to PM molecules, and decreases their efficiency.
According to the present invention there has now been developed a procedure by which dyes which are sensitive to polymerization initiators such as PM dyes, can be doped into composite glass, thus leading to high quality, solid state dye lasers.
More specifically, according to the present invention there is now provided a process for preparing a solid state dye laser in a composite glass matrix, without the use of polymerization initiators, comprising:
In especially preferred embodiments of the present invention said dye is a pyrromethene dye.
Preferably said heat polymerization is carried out in a closed container for a period of at least 5 days at a temperature of at least 63.degree. C. and there is formed a final product having a density of between 1.4 and 1.5 gm/cm.sup.3.
In especially preferred embodiments of the present invention there is formed a final product emitting light pulses at 560-575 nm and having a laser slope efficiency of about 42%.
While the invention will now be described in connection with certain preferred embodiments in the following examples and with reference to the accompanying figures so that aspects thereof may be more fully understood and appreciated, it is not intended to limit the invention to these particular embodiments. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the scope of the invention as defined by the appended claims. Thus, the following examples which include preferred embodiments will serve to illustrate the practice of this invention, it being understood that the particulars shown are by way of example and for purposes of illustrative discussion of preferred embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of formulation procedures as well as of the principles and conceptual aspects of the invention.